1. Field of the Invention
The present invention relates to an image reading method and an apparatus for the same and more particularly to the image reading method and the image reading apparatus being capable of simultaneously reading a plurality of lines to be read (“line to be read” hereinafter being referred to as a “reading line” by using a CCD (Charge-Coupled Device).
The present application claims priority of Japanese Patent Application No. 2000-124066 filed on Apr. 25, 2000, which is hereby incorporated by reference.
2. Description of the Related Art
A conventional image reading apparatus (such as a scanner) is so configured that an original document can be read by using a string of light sensing devices being placed in a line and making up a monochrome CCD having pixels the number of which is enough to receive light reflected off each of reading lines of the original document and, therefore, in order to read the entire original document by such the conventional image reading apparatus, as shown in FIG. 17, it is necessary to read each reading line of the original document, by using the string of light sensing devices, in a sub-scanning direction. FIG. 17 is a diagram explaining operations of reading the original document by using the conventional image reading apparatus. In FIG. 17, a mark “A” shows a reading line of the original document and each of marks A1, A2, . . . shows an image signal obtained by reading the reading line of the original document. Speedups in reading the original document are generally and conventionally realized by shortening time spent on scanning one reading line (hereafter referred to as a “reading time”), that is, by reducing time during which signal electrical charges are accumulated in a light receiving section within the CCD.
However, reduction of the time for accumulating the signal electrical charges leads to a decrease in amounts of stored light, thus causing adverse effects by noises or a like. In order to reduce the time for accumulating signal electrical charges without decreasing the amount of the stored light, two methods are available; one is to increase an amount of light emitted from a light source in response to a rise of a reading speed and an other is to increase a sensitivity of the CCD.
However, the above two methods have problems. If the amount of light emitted from the light source is increased in response to the rise in the reading speed, problems of an increase in power consumption and of heat production occur and therefore the method is not economical and a measure against the heat production in the light source is needed, while, if the sensitivity of the CCD has to be increased, not only the fabrication of the CCD having high sensitivity is not easy, but also use of a costly CCD is needed. Moreover, as the speed of the reading is made higher, speedup of data processing in other related circuits of the image reading apparatus is required and therefore use of high-speed circuits is needed, thus causing costs of other circuits to become high.